1. The Technical Field
The present invention is directed to methods and apparatus for interconnecting a field effect sensor with a control system or controlled device using only two wires.
2. The Prior Art
Mechanical switches are sometimes used to detect change in position of a mechanical part or level of a fluid, among other things. Such uses are particularly prevalent in automotive applications. For example, mechanical switches have long been used in automobiles to sense parameters such as throttle position and windshield washer fluid level.
Although mechanical switches have been refined extensively over the years, they nevertheless are inherently prone to failure because they include moving parts. Further, such switches are often used in connection with mechanical linkages which also are inherently prone to failure and which add cost, weight, and complexity.
Field effect sensors have been used as replacements for mechanical switches in many applications. Indeed, field effect sensors can be used to sense proximity of a mechanical part or a liquid. Field effect sensors have many advantages over mechanical switches. For example, they have no moving parts which can wear out or break. Also, they can be inexpensively mass-produced and customized for use in applications that would not readily accommodate mechanical switches.
Mechanical switches in their simplest form are two-wire (input and output) devices that mechanically make or break an electrical circuit. They operate using mechanical force and do not require electrical power for their operation. Conversely, field effect sensors are solid state-devices which require electrical power for their operation. Accordingly, a field effect sensor typically requires at least one more wire for its operation than does a mechanical switch. As such, known field effect sensors typically cannot be used as drop-in replacements for mechanical switches without some modification to the apparatus into which they would be installed.